I like this Kensington Bluetooth USB Micro Adapter as it is small enough to remain in your laptop to be stored in a bag without having to detach it or run the risk of breaking it on your travels. On the flipside, it is probably too small for most, and that makes it the perfect candidate to be misplaced wherever you go. It complies with Bluetooth 2.0+ EDR and supports A2DP wireless stereo streaming for those who cannot live without music. If your laptop does not yet have Bluetooth capability (because you were to cheap to realize your folly), the Kensington Bluetooth USB Micro Adapter can be picked up for $40.
ER: i saw this thing last month in Tokyo, quite cheap.. but all the modern fullsize notebooks have BT built-in i hope they have a Linux driver so that i can use it with my EEE PC